Communication device, communication method, and communication system

ABSTRACT

A communication device is connected to first and second networks. The communication device includes a processor executing a process including relaying communication between the first and second networks; and confirming connection to a first device connected to the first network or a second device connected to the second network, based on a device list registered in advance. The confirming includes blocking the relaying when the confirmation of the connection to the first device is unsuccessful; enabling the relaying when the confirmation of the connection to the first device is successful and when the second device is not registered in the device list; enabling the relaying when the confirmation of the connections to the first and second devices is successful; and blocking the relaying when the confirmation of the connection to the first device is successful and when the confirmation of the connection to the second device is unsuccessful.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. § 119 toJapanese Patent Application No. 2017-063268, filed on Mar. 28, 2017, thecontents of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a communication device, a communicationmethod, and a communication system.

2. Description of the Related Art

In government offices or hospitals, there are cases where a plurality ofnetworks are used, including a network handling information to be keptconfidential such as personal information, and a network requiring lessconfidentiality than the aforementioned network. Also, in a generalcompany, even when a plurality of departments share the same floor, thenetworks used by the respective departments may be different. When aplurality of networks are operated, and a multifunction peripheral or aprinter is installed for each network, the management cost increases andthe occupied area increases. Thus, it is required to consolidate thenumber of multifunction peripherals or printers. However, when onemultifunction peripheral or one printer processes packets from aplurality of networks, in the rout control by Transmission ControlProtocol/Internet Protocol (TCP/IP), problems in security may occur,such as erroneous transmission and leakage of packets to other networks(for example, communication from a terminal having the same InternetProtocol (IP) address that is disguised, etc.), etc. There is alreadyknown a configuration of providing an image processing apparatus capableof automatically enabling communication, when it is necessary to performcommunication between the image processing apparatus and another device,even when the network interface of the image processing apparatusbelongs to a particular network address, and the other device that is acommunication partner of the image processing apparatus belongs to anetwork address different from the particular network address (forexample, Patent Document 1).

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2005-229332

SUMMARY OF THE INVENTION

An aspect of the present invention provides a communication device, acommunication method, and a communication system, in which one or moreof the disadvantages of the related art are reduced.

According to one aspect of the present invention, there is provided acommunication device connected to a first network and a second network,the communication device including a processor, in communication with amemory, executing a process including relaying communication between thefirst network and the second network via a network interface included inthe communication device; and confirming connection to a first deviceconnected to the first network or a second device connected to thesecond network, based on a device list stored in advance in a storagedevice included in the communication device, the connection to the firstdevice or the second device being made via a port included in thecommunication device, wherein the confirming includes blocking therelaying upon determining that the confirmation of the connection to thefirst device connected to the first network is unsuccessful based on thedevice list; enabling the relaying upon determining that theconfirmation of the connection to the first device connected to thefirst network is successful based on the device list and upondetermining that the second device connected to the second network isnot registered in the device list; enabling the relaying upondetermining that the confirmation of the connection to the first deviceconnected to the first network is successful based on the device listand upon determining that the confirmation of the connection to thesecond device connected to the second network is successful based on thedevice list; and blocking the relaying upon determining that theconfirmation of the connection to the first device connected to thefirst network is successful based on the device list and upondetermining that the confirmation of the connection to the second deviceconnected to the second network is unsuccessful based on the devicelist.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration example of acommunication system according to an embodiment of the presentinvention;

FIG. 2 an example of a hardware block diagram of a relay deviceaccording to an embodiment of the present invention;

FIG. 3 is an example of a functional block diagram of the relay deviceaccording to an embodiment of the present invention;

FIG. 4 is a sequence diagram for describing an example of a confirmationprocedure executed by the relay device according to an embodiment of thepresent invention; and

FIGS. 5A through 5D are diagrams illustrating display examples of adisplay unit according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The network device of the related art can separate a plurality ofnetworks that are not permitted to communicate with each other. On theother hand, a particular network (a network to which a multifunctionperipheral, etc., which is desired to be commonly used, is connected)can communicate with each of the plurality of networks that are notpermitted to communicate with each other. Therefore, there has been aproblem that when a Local Area Network (LAN) cable is physicallyinserted by mistake, communicate will be enabled between the networksthat are not supposed to be permitted to communicate with each other.

A problem to be solved by an embodiment of the present invention is toprevent communication in a combination of networks for whichcommunication is not permitted, when a plurality of networks areseparated.

Embodiments of the present invention will be described by referring tothe accompanying drawings.

FIG. 1 is a diagram illustrating a configuration example of acommunication system 1000 according to an embodiment of the presentinvention. As illustrated in FIG. 1, the communication system 1000includes a relay device 100, a gateway (GW) 110, a personal computer(PC) 111, a GW 120, a PC 121, a confidential server 131, a confidentialinformation management PC 132, and a multifunction peripheral (MFP) 141.

The relay device 100 includes a plurality of physical Local Area Network(LAN) ports and relays communication between a plurality of networks.The plurality of networks may have different network addresses or mayhave the same network address. In the configuration example illustratedin FIG. 1, a port A of the relay device 100 is connected to a networkNet_MFP, and the network address of Net_MFP is set as 192.168.0.0/24.Similarly, a port B of the relay device 100 is connected to a networkNet_1, and the network address of Net_1 is set as 172.16.1.0/24.Similarly, a port C of the relay device 100 is connected to a networkNet_2, and the network address of Net_2 is set as 172.16.2.0/24.Similarly, a port D of the relay device 100 is connected to a networkNet_3, and the network address of Net_3 is set as 172.16.3.0/24. Therelay device 100 does not relay the communication between the networksconnected to the port B, the port C, and the port D, but relays thecommunication between each of the networks connected to the port B, theport C, and the port D and the network connected to the port A.

The GW 110 and the GW 120 are gateways. For example, when a devicetransmits a packet to an Internet Protocol (IP) address other than thenetwork address to which the device belongs, the gateway receives thepacket from the device and transmits the received packet to anothernetwork. The GW 110 is connected to Net_1 and has an IP address of172.16.1.1 and a Media Access Control (MAC) address ofuu:vv:ww:xx:yy:zz. The GW 120 is connected to Net_2, and has an IPaddress of 172.16.2.1 and a MAC address of 1a:2b:3c:4d:5e:6f.

The PC 111, the PC 121, and the confidential information management PC132 are personal computers (PCs). The PC 111 is connected to Net_1, thePC 121 is connected to Net_2, and the confidential informationmanagement PC 132 is connected to Net_3.

The confidential server 131 is a server computer. The confidentialserver 131 is connected to Net_3 and has an IP address of 172.16.3.10.

The MFP 141 is a multifunction peripheral. For example, the MFP 141 hasa plurality of functions such as functions of a printer and a scanner.The MFP 141 is connected to Net_MFP, and has an IP address of192.168.0.10 and a MAC address of aa:bb:cc:dd:ee:ff.

FIG. 2 an example of a hardware block diagram of the relay device 100according to an embodiment of the present invention. The relay device100 of FIG. 2 includes a Central Processing Unit (CPU) 1001, a networkinterface 1002, an input/output interface 1003, a secondary storagedevice 1004, and a memory device 1005, etc., which are mutuallyconnected.

The programs for implementing the processes by the relay device 100 arestored in the secondary storage device 1004. The secondary storagedevice 1004 stores installed programs and necessary files and data, etc.

The memory device 1005 reads out a program from the secondary storagedevice 1004 and stores the program when an instruction to activate theprogram is issued. The CPU 1001 implements functions relating to therelay device 100 according to a program stored in the memory device1005.

The network interface 1002 is an interface for communicating with adevice connected to a port. The port may be a wired LAN port or a portusing another communication method.

The input/output interface 1003 is an interface for connecting withvarious input/output devices such as a Universal Serial Bus (USB)device, a hardware key, a status notification Light Emitting Diode(LED), and a liquid crystal display, etc.

Note that the GW 110, the GW 120, the PC 111, the PC 121, theconfidential information management PC 132, the confidential server 131,and the MFP 141 may have the same hardware configuration as in FIG. 2.

FIG. 3 is an example of a functional block diagram of the relay device100 according to an embodiment of the present invention. As illustratedin FIG. 3, the relay device 100 includes an inflow port determining unit11, a relay unit 12, a connection confirming unit 13, a connectionconfirmation list storage unit 14, a timekeeping unit 15, and a displayunit 16. These units are implemented by a process that one or moreprograms installed in the relay device 100 cause the CPU 1001 toexecute.

When a packet flows into the relay device 100 via a port, the inflowport determining unit 11 determines the port in which the packet hasflowed, among the ports A to D. The relay unit 12 relays communicationbetween the port A and the port B, the port C, or the port D. Forexample, at the time of activation, the connection confirming unit 13checks whether the cable connection to the port has been set in advance.Furthermore, the connection confirming unit 13 transmits a responseconfirmation message to each port, and analyzes a received responsemessage. The connection confirmation list storage unit 14 storesconnection confirmation destination information used for theconfirmation of connection by the connection confirming unit 13. Thetimekeeping unit 15 measures a predetermined time. The display unit 16displays the operation status of the relay unit 12.

Note that each of the devices forming the GW 110, the GW 120, the PC111, the PC 121, the confidential server 131, the confidentialinformation management PC 132, and the MFP 141 includes at least aresponding unit for receiving a response confirmation messagetransmitted from the relay device 100 and transmitting a response to therelay device 100, and a communication unit for the devices tocommunicate with each other.

FIG. 4 is a sequence diagram for describing an example of a confirmationprocedure executed by the relay device 100 according to an embodiment ofthe present invention. In the sequence illustrated in FIG. 4, theconnection confirmation of a device connected to a LAN port is executedbased on whether the MAC addresses completely match, and the relaydevice 100 permits the relay of the communication relating to thecorresponding LAN port. FIG. 4 illustrates, for example, a confirmationprocedure executed by the relay device 100 at the time of activation;however, the execution of the confirmation procedure is not limited tothe time of activation. The confirmation procedure illustrated in FIG. 4may be executed at any timing.

In step S101, the connection confirming unit 13 transmits a list requestto the connection confirmation list storage unit 14. Subsequently, theconnection confirmation list storage unit 14 transmits a list responseto the connection confirming unit 13 (step S102). Table 1 is an exampleof the connection confirmation list stored in the connectionconfirmation list storage unit 14.

TABLE 1 LAN PORT LABEL IP ADDRESS MAC ADDRESS LAN PORT A MFP192.168.0.10 aa:bb:cc:dd:ee:ff (ESSENTIAL) LAN PORT B GW1 172.16.1.1uu:vv:ww:xx:yy:zz (OPTIONAL) LAN PORT C GW2 172.16.2.1 1a:2b:3c:4d:5e:6f(OPTIONAL) LAN PORT D — — — (OPTIONAL)

As indicated in Table 1, for each device, “LAN port”, “label”, “IPaddress”, and “MAC address” are stored in association with each other.(Essential) or (optional) described in the column “IP address” indicateswhether the IP address is essential in the list. For example, for “LANport A”, it is indicated that a device for which “label” is “MFP”, “IPaddress” is “192.168.0.10”, and the MAC address is “aa:bb:cc:dd:ee:ff”is a device for which relay of communication by the relay device 100 ispermitted. Similarly, for “LAN port B”, it is indicated that a devicefor which “label” is “GW 1”, “IP address” is “172.16.1.1”, and the MACaddress is “uu:vv:ww:xx:yy:zz” is a device for which relay ofcommunication by the relay device 100 is permitted. Similarly, for “LANport C”, it is indicated that a device for which “label” is “GW 2”, “IPaddress” is “172.16.2.1”, and the MAC address is “1a:2b:3c:4d:5e:6f” isa device for which relay of communication by the relay device 100 ispermitted. Note that for “LAN port D”, the descriptions of the label,the IP address, and the MAC address are blank, indicating that a deviceconnected to the LAN port D is a device for which relay of communicationby the relay device 100 is permitted in advance.

In step S103, the connection confirming unit 13 transmits an MFPconfirmation request to the LAN port A based on the connectionconfirmation list received in step S102. Subsequently, a responseconfirmation message is transmitted from the LAN port A to the MFP 141(step S104). Subsequently, the MFP 141 transmits, via the LAN port A(step S105), a response message to the connection confirming unit 13(step S106).

In step S107, the connection confirming unit 13 compares the MAC addressincluded in the response message with the MAC address“aa:bb:cc:dd:ee:ff” associated with the label “MFP” for the LAN port Aincluded in the connection confirmation list. When the MAC addressesmatch, the process proceeds to step S108. Conversely, when the MACaddresses do not match, or when no response message is received, thecommunication relating to the LAN port A is blocked. At this time, therelay device 100 may abort the sequence illustrated in FIG. 4.

In step S108, the connection confirming unit 13 transmits a relaypermission to the relay unit 12. Subsequently, the relay unit 12 enablesthe communication between the LAN port A and the LAN port D (step S109).In step S110, the connection confirming unit 13 transmits a displayinstruction to the display unit 16. Subsequently, the display unit 16changes the display (step S111).

FIGS. 5A through 5D are diagrams illustrating display examples of thedisplay unit 16 according to an embodiment of the present invention. Adisplay example 1 illustrated in FIG. 5A is an example where a state inwhich relaying is not performed is displayed on the display unit 16.Table 2 is a table indicating the state of display example 1 illustratedin FIG. 5A.

TABLE 2 RELAY LAN PORT RELAY STATE BETWEEN LAN PORT A AND LAN PORT B xBETWEEN LAN PORT A AND LAN PORT C x BETWEEN LAN PORT A AND LAN PORT D x

As indicated in Table 2, communication between LAN port A and LAN portB, communication between LAN port A and LAN port C, and communicationbetween LAN port A and LAN port D are not relayed. The state indicatedin Table 2 is, for example, the initial state of the relay device 100.That is, at the time of step S101 illustrated in FIG. 4, the displayunit 16 may display the display example 1 illustrated in FIG. 1.Furthermore, the state indicated in Table 2 is, for example, a state inwhich the connection confirming unit 13 could not confirm a responsemessage from the MFP 141.

Table 3 is a table indicating a state of a display example 2 illustratedin FIG. 5B.

TABLE 3 RELAY LAN PORT RELAY STATE BETWEEN LAN PORT A AND LAN PORT B xBETWEEN LAN PORT A AND LAN PORT C x BETWEEN LAN PORT A AND LAN PORT D ∘

The display example 2 illustrated in FIG. 5B is an example where a statein which only the communication between the LAN port A and the LAN portD is relayed, is displayed on the display unit 16. That is, as indicatedin Table 3, communication between the LAN port A and the LAN port B andcommunication between the LAN port A and the LAN port C are not relayed,but communication between the LAN port A and the LAN port D is relayed.In the state indicated in Table 3, for example, the connectionconfirming unit 13 has confirmed a response message from the MFP 141.

Table 4 is a table indicating the state of a display example 3illustrated in FIG. 5C.

TABLE 4 RELAY LAN PORT RELAY STATE BETWEEN LAN PORT A AND LAN PORT B ∘BETWEEN LAN PORT A AND LAN PORT C x BETWEEN LAN PORT A AND LAN PORT D ∘

The display example 3 illustrated in FIG. 5C is an example where a statein which communication between the LAN port A and the LAN port B andcommunication between the LAN port A and the LAN port D are relayed, isdisplayed on the display unit 16. That is, as indicated in Table 4,communication between the LAN port A and the LAN port C is not relayed,but communication between the LAN port A and the LAN port B andcommunication between the LAN port A and the LAN port D are relayed. Inthe state indicated shown in Table 4, for example, the connectionconfirming unit 13 has confirmed a response message from the MFP 141 andthe GW 110.

Table 5 is a table indicating the state of a display example 4illustrated in FIG. 5D.

TABLE 5 RELAY LAN PORT RELAY STATE BETWEEN LAN PORT A AND LAN PORT B ∘BETWEEN LAN PORT A AND LAN PORT C ∘ BETWEEN LAN PORT A AND LAN PORT D ∘

A display example 4 illustrated in FIG. 5D is an example where a statein which communication between the LAN port A and the LAN port B,communication between the LAN port A and the LAN port C, andcommunication between the LAN port A and the LAN port D is relayed, aredisplayed on the display unit 16. That is, as indicated in Table 5,communication between the LAN port A and the LAN port B, communicationbetween the LAN port A and the LAN port C, and communication between theLAN port A and the LAN port D are relayed. In the state indicated inTable 5, for example, the connection confirming unit 13 has confirmed aresponse message from the MFP 141, the GW 110, and the GW 120.

Referring back to FIG. 4, in step S111, the display unit 16 changes thedisplay from the display example 1 to the display example 2 illustratedin FIG. 5B. That is, the display unit 16 displays a state in whichcommunication between the LAN port A and the LAN port D is relayed.

In step S112, the connection confirming unit 13 transmits a GW 110confirmation request to the LAN port B based on the connectionconfirmation list received in step S102. Subsequently, a responseconfirmation message is transmitted from the LAN port B to the GW 110(step S113). Subsequently, the GW 110 transmits, via the LAN port B(step S114), a response message to the connection confirming unit 13(step S115).

In step S116, the connection confirming unit 13 compares the MAC addressincluded in the response message with the MAC address“uu:vv:ww:xx:yy:zz” associated with the label “GW 1” for the LAN port Bincluded in the connection confirmation list. When the MAC addressesmatch, the connection confirming unit 13 determines that the connectionconfirmation has been successful, and proceeds to step S117. Conversely,when the MAC addresses do not match, or when a response message is notreceived, the connection confirming unit 13 determines that theconnection confirmation has been unsuccessful and blocks thecommunication relating to the LAN port B. At this time, the relay device100 may abort the sequence illustrated in FIG. 4.

In step S117, the connection confirming unit 13 transmits a relaypermission to the relay unit 12. Subsequently, the relay unit 12 enablesthe communication between the LAN port A and the LAN port B (step S118).In step S119, the connection confirming unit 13 transmits a displayinstruction to the display unit 16. Subsequently, the display unit 16changes the display from the display example 2 to the display example 3illustrated in FIG. 5C (step S120). That is, the display unit 16displays a state in which communication between the LAN port A and theLAN port B and communication between the LAN port A and the LAN port Dare relayed.

In step S121, the connection confirming unit 13 transmits a GW 120confirmation request to the LAN port B based on the connectionconfirmation list received in step S102. Subsequently, a responseconfirmation message is transmitted from the LAN port C to the GW 120(step S122). Subsequently, the GW 120 transmits, via the LAN port C(step S123), a response message to the connection confirming unit 13(step S124).

In step S125, the connection confirming unit 13 compares the MAC addressincluded in the response message with the MAC address“1a:2b:3c:4d:5e:6f” associated with the label “GW 2” for the LAN port Cincluded in the connection confirmation list. When the MAC addressesmatch, the connection confirming unit 13 determines that the connectionconfirmation has been successful, and proceeds to step S126. Conversely,when the MAC addresses do not match, or when a response message is notreceived, the connection confirming unit 13 determines that theconnection confirmation has been unsuccessful and blocks thecommunication relating to the LAN port C. At this time, the relay device100 may abort the sequence illustrated in FIG. 4.

In step S126, the connection confirming unit 13 transmits a relaypermission to the relay unit 12. Subsequently, the relay unit 12 enablescommunication between the LAN port A and the LAN port C (step S127). Instep S128, the connection confirming unit 13 transmits a displayinstruction to the display unit 16. Subsequently, the display unit 16changes the display from the display example 3 to the display example 4illustrated in FIG. 5D (step S129). That is, the display unit 16displays a state in which communication between the LAN port A and theLAN port B, communication between the LAN port A and the LAN port C, andcommunication between the LAN port A and the LAN port D are relayed.

In step S130, the connection confirming unit 13 transmits a timekeepinginstruction to the timekeeping unit 15. Subsequently, the timekeepingunit 15 starts timekeeping (step S131). Upon the elapse of apredetermined time after starting the timekeeping, a time elapse reportis transmitted to the connection confirming unit 13 (step S132).

In step S133, the connection confirming unit 13 proceeds to step S101 inorder to start the confirmation procedure again. That is, when apredetermined time has elapsed after the execution of the confirmationprocedure, the confirmation procedure is executed again. Furthermore,the confirmation procedure may be repeated at regular time intervals. Bythe above steps, the confirmation procedure executed by the relay device100 is completed.

Note that in the sequence illustrated in FIG. 4, the connectionconfirming unit 13 executes the connection confirmation of a deviceconnected to a LAN port based on the complete matching of the MACaddresses. However, the connection confirming method is not limited tothe complete matching of MAC addresses. For example, the connectionconfirmation method indicated in Table 6 may be used.

TABLE 6 METHOD OF RESPONSE DETERMINATION BY CONFIRMING CONFIRMATIONRESPONSE CONNECTION CONNECTION MESSAGE MESSAGE CONFIRMING UNIT 13 pingRESPONSE ICMP ECHO ICMP ECHO WHETHER ECHO CONFIRMATION REQUEST RESPONSERESPONSE IS NORMAL MAC ADDRESS arp request arp reply WHETHER LEADINGVENDOR PART THREE BYTES ARE OF A MATCHING PARTICULAR VENDOR MAC ADDRESSarp request arp reply WHETHER MAC ADDRESS COMPLETE COMPLETELY MATCHESADDRESS MATCHING SET IN ADVANCE IN TABLE 1 ACQUIRE SNMP SNMP WHETHERTHERE IS OID OF EXTENDED MIB Get-Request Get-Response PARTICULAR VENDORPORT SCANNING CONNECTION CONNECTION WHETHER A PARTICULAR REQUESTRESPONSE PORT IS OPEN (PERMIT/REJECT)

As indicated in Table 6, when the connection confirmation method is“ping response confirmation”, “ICMP echo request” is used as theresponse confirmation message and “ICMP echo response” is used as theresponse message. The connection confirming unit 13 determines whetherthe echo response is normal.

As indicated in Table 6, when the connection confirmation method is “MACaddress vendor part match”, “arp request” is used as the responseconfirmation message and “arp reply” is used as the response message.The connection confirming unit 13 determines whether the leading threebytes of the MAC address included in arp reply are of a particularvendor. That is, the relay device 100 can permit relaying with respectto a device of a particular vendor.

As indicated in Table 6, when the connection confirmation method is “MACaddress complete matching”, “acp request” is used as the responseconfirmation message and “arp reply” is used as the response message.The connection confirming unit 13 determines whether the MAC addresscompletely matches the MAC address set in advance in the connectionconfirmation list indicated in Table 1.

As indicated in Table 6, when the connection confirmation method is“acquire extended MIB”, “Simple Network Management Protocol (SNMP)Get-Request” is used as the response confirmation message and “SNMPGet-response” is used as the response message. The connection confirmingunit 13 determines whether an Object Identifier (OID) of a particularvender exists among the OIDs included in the SNMP Get-Response. That is,the relay device 100 can permit relaying with respect to a device of aparticular vendor. Furthermore, the OID is setting information set inthe device in advance, and the possibility of a change in the OID isrelatively low compared to a MAC address.

As indicated in Table 6, when the connection confirmation method is“port scanning”, “connection request” is used as the responseconfirmation message, and “connection response (permit/reject)” is usedas the response message. The connection confirming unit 13 determineswhether a particular port is open. The “connection request” may be aTransmission Control Protocol (TCP) packet or a User Datagram Protocol(UDP) packet.

As described above, according to an embodiment of the present invention,the relay device 100 confirms the connection of each of the devicesconnected to a plurality of networks, based on the connectionconfirmation list registered in advance, and then permits the relayingof the network. Therefore, when an unintended physical connection ismade, relaying of the network is not permitted. Therefore, when aplurality of networks are separated, it is possible to preventcommunication in a combination of networks for which communication isnot permitted.

In the embodiment of the present invention, the network Net_MFP is anexample of a first network. The network Net_1, the network Net_2, or thenetwork Net_3 is an example of a second network. The relay device 100 isan example of a communication device. The connection confirming unit 13is an example of a confirming unit. The connection confirmation list isan example of a device list. An IP address is an example of a logicaladdress. The ping response is an example of an echo response. The MACaddress is an example of a physical address. The leading three bytes ofthe MAC address indicating the vendor of the device are an example of apart of the physical address. SNMP is an example of a network managementprotocol. The OID is an example of an identifier on the networkmanagement protocol. The MFP 141 is an example of an image processingdevice. The PC 111 is an example of an information processing device.

According to one embodiment of the present invention, it is possible toprevent communication in a combination of networks for whichcommunication is not permitted, when a plurality of networks areseparated.

The communication device, the communication method, and thecommunication system are not limited to the specific embodimentsdescribed in the detailed description, and variations and modificationsmay be made without departing from the spirit and scope of the presentinvention.

What is claimed is:
 1. A communication device connected to a firstnetwork and a second network, the communication device comprising aprocessor, in communication with a memory, executing a processincluding: relaying communication between the first network and thesecond network via a network interface included in the communicationdevice; and confirming connection to a first device connected to thefirst network or a second device connected to the second network, basedon a device list stored in advance in a storage device included in thecommunication device, the connection to the first device or the seconddevice being made via a port included in the communication device,wherein the confirming includes: blocking the relaying upon determiningthat the confirmation of the connection to the first device connected tothe first network is unsuccessful based on the device list; enabling therelaying upon determining that the confirmation of the connection to thefirst device connected to the first network is successful based on thedevice list and upon determining that the second device connected to thesecond network is not registered in the device list; enabling therelaying upon determining that the confirmation of the connection to thefirst device connected to the first network is successful based on thedevice list and upon determining that the confirmation of the connectionto the second device connected to the second network is successful basedon the device list; and blocking the relaying upon determining that theconfirmation of the connection to the first device connected to thefirst network is successful based on the device list and upondetermining that the confirmation of the connection to the second deviceconnected to the second network is unsuccessful based on the devicelist.
 2. The communication device according to claim 1, wherein alogical address, associated with each of the first device and the seconddevice, is registered in the device list, and the confirming includesconfirming the connection to the first device or the second deviceaccording to an echo response for which a transmission destination isidentified by the logical address.
 3. The communication device accordingto claim 1, wherein a logical address and a physical address, associatedwith each of the first device and the second device, are registered inthe device list, and the confirming includes confirming the connectionto the first device or the second device by acquiring, from the firstdevice or the second device for which the confirmation is being made,the physical address based on the logical address, and matching theacquired physical address to the physical address registered in thedevice list.
 4. The communication device according to claim 3, wherein apart of the physical address, associated with each of the first deviceand the second device, is specified in advance, and the confirmingincludes confirming the connection to the first device or the seconddevice by matching a part of the acquired physical address to the partof the physical address specified in advance.
 5. The communicationdevice according to claim 1, wherein an identifier, which is on anetwork management protocol associated with each of the first device andthe second device, is specified in advance, and the confirming includesconfirming the connection to the first device or the second device byacquiring an identifier included in a response according to the networkmanagement protocol, and matching the acquired identifier to theidentifier specified in advance.
 6. The communication device accordingto claim 1, wherein the processor executes the process furtherincluding: displaying, on a display, a state of the relaying beingenabled or a state of the relaying being blocked.
 7. The communicationdevice according to claim 1, wherein the confirming includes confirmingagain the connection to the first device connected to the first networkand the connection to the second device connected to the second network,upon determining that a predetermined time has elapsed from a time pointwhen the relaying has been enabled or blocked.
 8. A communication methodexecuted by a computer included in communication device connected to afirst network and a second network, the communication method comprising:relaying communication between the first network and the second networkvia a network interface included in the communication device; andconfirming connection to a first device connected to the first networkor a second device connected to the second network, based on a devicelist stored in advance in a storage device included in the communicationdevice, the connection to the first device or the second device beingmade via a port included in the communication device, wherein theconfirming includes: blocking the relaying upon determining that theconfirmation of the connection to the first device connected to thefirst network is unsuccessful based on the device list; enabling therelaying upon determining that the confirmation of the connection to thefirst device connected to the first network is successful based on thedevice list and upon determining that the second device connected to thesecond network is not registered in the device list; enabling therelaying upon determining that the confirmation of the connection to thefirst device connected to the first network is successful based on thedevice list and upon determining that the confirmation of the connectionto the second device connected to the second network is successful basedon the device list; and blocking the relaying upon determining that theconfirmation of the connection to the first device connected to thefirst network is successful based on the device list and upondetermining that the confirmation of the connection to the second deviceconnected to the second network is unsuccessful based on the devicelist.
 9. The communication method according to claim 8, wherein alogical address, associated with each of the first device and the seconddevice, is registered in the device list, and the confirming includesconfirming the connection to the first device or the second deviceaccording to an echo response for which a transmission destination isidentified by the logical address.
 10. The communication methodaccording to claim 8, wherein a logical address and a physical address,associated with each of the first device and the second device, areregistered in the device list, and the confirming includes confirmingthe connection to the first device or the second device by acquiring,from the first device or the second device for which the confirmation isbeing made, the physical address based on the logical address, andmatching the acquired physical address to the physical addressregistered in the device list.
 11. The communication method according toclaim 10, wherein a part of the physical address, associated with eachof the first device and the second device, is specified in advance, andthe confirming includes confirming the connection to the first device orthe second device by matching a part of the acquired physical address tothe part of the physical address specified in advance.
 12. Thecommunication method according to claim 8, wherein an identifier, whichis on a network management protocol associated with each of the firstdevice and the second device, is specified in advance, and theconfirming includes confirming the connection to the first device or thesecond device by acquiring an identifier included in a responseaccording to the network management protocol, and matching the acquiredidentifier to the identifier specified in advance.
 13. The communicationdevice according to claim 8, further comprising: displaying, on adisplay, a state of the relaying being enabled or a state of therelaying being blocked.
 14. The communication method according to claim8, wherein the confirming includes confirming again the connection tothe first device connected to the first network and the connection tothe second device connected to the second network, upon determining thata predetermined time has elapsed from a time point when the relaying hasbeen enabled or blocked.
 15. A communication system comprising: acommunication device connected to a first network and a second network;an image processing device connected to the first network; and aninformation processing device connected to the second network, whereinthe image processing device includes a first processor, in communicationwith a first memory, executing a first process including: responding toa connection confirmation transmitted from the communication device; andcommunicating with the information processing device, whereininformation processing device includes a second processor, incommunication with a second memory, executing a second processincluding: responding to a connection confirmation transmitted from thecommunication device; and communicating with the image processingdevice, and wherein the communication device includes a third processor,in communication with a third memory, executing a third processincluding: relaying communication between the image processing deviceand the information processing device via a network interface includedin the communication device; and confirming connection to the imageprocessing device or the information processing device, based on adevice list stored in advance in a storage device included in thecommunication device, the connection to the image processing device orthe information processing device being made via a port included in thecommunication device, wherein the confirming includes: blocking therelaying upon determining that the confirmation of the connection to theimage processing device is unsuccessful based on the device list;enabling the relaying upon determining that the confirmation of theconnection to the image processing device is successful based on thedevice list and upon determining that the information processing deviceis not registered in the device list; enabling the relaying upondetermining that the confirmation of the connection to the imageprocessing device is successful based on the device list and upondetermining that the confirmation of the connection to the informationprocessing device is successful based on the device list; and blockingthe relaying upon determining that the confirmation of the connection tothe image processing device is successful based on the device list andupon determining that the confirmation of the connection to theinformation processing device is unsuccessful based on the device list.